Fig. 9. Mammillary body neurons survive until the end of gestation in Sim1/Sim2 double mutants. Coronal sections through the MB of E18.5 with various dosage of Sim1/Sim2, as indicated, hybridized with Sim1 (A,B), Lhx1 (C,D) and Foxb1 (E-H) probes. Sim1 and Lhx1 expression is maintained in the MB of Sim1/Sim2 double mutants. By contrast, Foxb1 expression is dramatically reduced in Sim1/Sim2 double mutants but not in embryos with at least one allele of Sim1/Sim2. Of note, the apparent smaller sizes of the MBs shown in G and H reflect different planes of section.